1. Field of the Invention
The present invention relates to an extramedullary femoral clamp guide system for total knee arthroplasty that enables cutting a portion of the distal end of a femur perpendicularly to an ideal weight bearing axis of the femur as viewed in an antero-posterior image of the femur and cutting a portion of the frontal surface of a distal end part of the femur in parallel to he frontal surface of the distal end part of the femur.
2. Description of the Related Art
There are two systems for determining the angular position of a femoral component in total knee arthroplasty, i.e., an intramedullary guide system that inserts a rod into the medullary cannel of a femur, and an extramedullary guide system that connects a rod to a femur cutting guide, places the rod on the skin of the thigh and determines a cutting angle with respect to the femoral head as a landmark by using an X-ray image during operation.
The intramedullary guide system uses the anatomical morphology of the femur. It is reported in reports on clinical results of total knee arthroplasty that the intramedullary guide system is excellent in the accuracy of cutting angle.
The extramedullary guide system selects the femoral head as a landmark indirectly from an X-ray image during operation. Therefore, it is difficult to determine the center of the femoral head accurately. It is reported in reports on clinical results of the extramedullary guide system that cutting angle contains a large error.
An instrument for determining the mechanical axis of the femur with respect to the knee disclosed in JP-A No. Hei 8-33662 applies a tensile force to a distal end portion of the femur while the thigh is suspended by a suspender to determine an ideal weight bearing axis.
In the current total knee arthroplasty, the intramedullary guide system is used prevalently because the intramedullary guide system is superior in the accuracy of cutting angle to the extramedullary guide system.
Although the intramedullary guide system is excellent in the accuracy of cutting angle, the decision of a rod inserting portion and rod inserting angle is dependent mostly on the intuition of the surgeon. When an intramedullary guide inserting portion has bone spines, the rod inserting angle is prone to contain an error. Since the position of the tip of the rod is not fixed when the medullary canal is wide, cutting angle is prone to contain an error.
The intramedullary guide system cannot be applied to a curved or warped femur because it is difficult to insert the intramedullary rod into the medullary canal of a curved or warped femur.
It is reported that the bone is chipped when a guide is inserted in the distal end part of a femur for the intramedullary guide system, the normal circulation of the blood is obstructed due to the crushing and destruction of femoral medullary tissues, and serious fat embolism that cause sudden obstruction of blood vessels of the principal organs is created by the intramedullary guide system.
The invention disclosed in JP-A No. Hei 8-33662 needs a special suspender for suspending the entire leg, a device for fixedly holding the suspender on an operating table and troublesome operations, and hence the operation takes time. Furthermore, it is possible that a clean operating field becomes unclean because the position of the leg is unstable and the clean suspender is inserted through the unclean fixing device into the clean operating field.